Abstract
As high-precision flexible printed circuit boards (FPCBs) are required in electronic products, it is necessary to study wet chemical etching to obtain precise FPCBs with a 16-μm line pitch. First, a π-shaped FPCB model with 16-μm line pitch is established using the finite element method. The evolution of the Cu etching profile and the concentration and velocity distribution of the CuCl2 solution are then analyzed. To analyze the influence of conveyor speed and nozzle spray pressure on the Cu etching profile, wet chemical etching was tested along a horizontally conveyed line with CuCl2 as the acid etchant. The resulting profiles were analyzed by scanning electron microscopy. The experimental results agreed well with the simulation results, and the Cu etching profile obviously depended on both the conveyor speed and nozzle spray pressure. In addition, increasing the conveyor speed under constant nozzle spray pressure (0.16 MPa or 0.17 MPa) decreased the etching depth and increased the etching factor. In particular, when the conveyor speed was set to 3.8 m/min and the nozzle spray pressure raised to 0.18 MPa, the fabricated FPCB had a line pitch of 16 μm, an etching depth of 7.55 μm, and an etching factor of 6.45. This method can aid the selection of parameters for the wet chemical etching process, enabling the future manufacture of high-precision FPCBs and complex FPCB circuits.
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*Provided by Jiangsu Leader-Tech Semiconductor.
References
S. Gupta, W.T. Navaraj, L. Lorenzelli, and R. Dahiya, Ultra-thin chips for high-performance flexible electronics. NPJ Flex. Electron. 2, 8 (2018).
D. Kang, H. Lee, J. Yousaf, and W. Nah, Analysis of transmission characteristics of three-layer flexible printed circuit board, in 2018 International Symposium on Electromagnetic Compatibility (2018), pp. 935–940.
H. Zuo and S. He, FPCB masked one-step etching large aperture mirror for LiDAR. J. Microelectromech. Syst. 29, 571 (2020).
T.H. Phung, J. Jeong, A.N. Gafurov, I. Kim, S.Y. Kim, H.J. Chung, Y. Kim, H.J. Kim, K.M. Kim, and T.M. Lee, Hybrid fabrication of LED matrix display on multilayer flexible printed circuit board. Flex. Print. Electron. 6, 024001 (2021).
J.C. Zhu, J. Yu, L. Yin, W. Yang, H. Liu, G.F. Wang, L.W. Wang, and W. Cai, A flexible micro direct methanol fuel cells array based on FPCB. Energy Convers. Manag. 258, 115469 (2022).
M. Pociask-Biały, Ion milling method for revealing the HgCdTe MBE-grown structure, in 2021 Selected Issues of Electrical Engineering and Electronics (2021), pp. 1–6.
M. Li and Y. Kuo, Electromigration of plasma etched copper lines of various widths and lengths. ECS Trans. 86, 41 (2018).
M. Huff, Recent advances in reactive ion etching and applications of high-aspect-ratio microfabrication. Micromachines 12, 991 (2021).
O.Çakır, Review of etchants for copper and its alloys in wet etching processes. Key Eng. Mater.364–366, 460 (2008).
S.H. Lee, I.S. Park, H.H. Choe, M.P. Hong, J.H. Seo, and P. Kim, Study on wet patterning of thin films in vertical-transfer wet station for thin-film-transistor manufacturing. J. Soc. Inf. Display 19, 380 (2011).
M. Itoh, T. Kinoshita, C. Koike, M. Takeuchi, K. Kawasaki, and Y. Aoyagi, Straight and smooth etching of GaN (1100) plane by combination of reactive ion etching and KOH wet etching techniques. Jpn. J. Appl. Phys. 45, 3988 (2006).
S.H. Cho, S.H. Kim, N.E. Lee, H.M. Kim, and Y.W. Nam, Micro-scale metallization on flexible polyimide substrate by Cu electroplating using SU-8 photoresist mask. Thin Solid Films 475, 68 (2005).
Y.C. Wu, Y.J. Huang, M.K. Chen, Y.L. Lin, and L.S. Jang, Fabrication and characterization of Cu-plated fine pitch patterns on flexible polyimide. Appl. Mech. Mater. 284, 118 (2013).
L.Y. Siow, W. Deng, Q.X. Zhang, T.C. Chai, C.G. Koh, D. Witarsa, X. Wang, H. Sun, T. Ando, T. Y. Tee, and J. Wong, Fine pitch Cu pillar wafer process development and seed layer etching characterization, in 2012 IEEE 14th Electronics Packaging Technology Conference (2012), pp. 755–758.
D. Yang, F. Dai, W. Zhang, G. Wang, and L. Cao, Process development of ultra-fine pitch high density micro bumps, in 2018 19th International Conference on Electronic Packaging Technology (2018), pp. 1500–1503.
T.K. Yeh, M.H. Tsai, M.Y. Wang, and C.K. Weng, Improved shape evolution of copper interconnects prepared by jet-stream etching. J. Appl. Electrochem. 38, 1495 (2008).
K. Matsumoto, H. Arai, S. Taniguchi, and A. Kikuchi, Etching rate of copper by CuCl2-HCl solution. J. Jpn. Inst. Electron. Packag. 5, 35 (2002).
O. Çakıra, H. Temel, and M. Kiyak, Chemical etching of Cu-ETP copper. J. Mater. Process. Technol. 162–163, 275 (2005).
S.M. Mirvakili, K. Broderick, and R.S. Langer, A new approach for micro-fabrication of printed circuit boards with ultra-fine traces. ACS Appl. Mater. Interface 11, 38 (2019).
K. Gao, H. Shen, Y. Liu, Y. Jiang, C. Zheng, Y. Li, S. Ren, and C. Huang, Enhanced etching rate of black silicon by Cu/Ni co-assisted chemical etching process. Mater. Sci. Semicon. Proc. 88, 250 (2018).
H. Ekinci, R.K. Dey, and B. Cui, Two-step potassium hydroxide etching to enhance aspect ratio in trench fabrication. J. Vac. Sci. Technol. B 37, 062001 (2019).
S. Wang, F. Ding, F. Wang, X. Wang, and H. Zou, Study on reducing side etching of copper microelectrode by multi-step etching process. Mater. Res. Express. 6, 126411 (2019).
B.W. Fon, H.B. Tan, and K.K. Yang, Characterization of copper etching process on micro leadless land grid array (ゼLLGA) via design of experiments approach, in 2008 33rd IEEE/CPMT International Electronics Manufacturing Technology Conference (2008), pp. 1–6.
D. Zhang, L. Wang, R. Jia, K. Tao, S. Jiang, H. Ge, B. Wang, Z. Gao, X. Li, M. Li, and Z. Jin, Improving the performance of PERC silicon solar cells by optimizing the surface inverted pyramid structure on large-area mono-crystalline silicon wafers. Mater. Sci. Semicon. Proc. 88, 250 (2022).
T. Liu, K. Yang, Z. Zhang, L. Yan, B. Huang, H. Li, C. Zhang, X. Jiang, and H. Yan, Hydrofluoric acid-based etching effect on surface pit, crack, and scratch and laser damage site of fused silica optics. Opt. Express 27, 10705 (2019).
Y. Chen, J. Qian, X. Guo, and Y. Xing, An adaptive octree level set simulation method of the wet etching process for the fabrication of micro structure on sapphire crystal, in 2021 IEEE 16th International Conference on Nano/Micro Engineered and Molecular Systems (2021), pp. 882–886.
A. Toifl, F. Rodrigues, L.F. Aguinsky, A. Hössinger, and J. Weinbub, Continuum level-set model for anisotropic wet etching of patterned sapphire substrates. Semicond. Sci. Technol. 36, 045016 (2021).
Y.C. Lam, J.C. Chai, P. Rath, H. Zheng, and V.M. Murukeshan, A fixed-grid method for chemical etching. Int. Commun. Heat Mass Transf. 31, 1123 (2004).
P. Rath and J.C. Chai, Modeling convection-driven diffusion-controlled wet chemical etching using a total-concentration fixed-grid method. Numer. Heat Trans. B Fundam. 53, 143 (2007).
C.B. Shin and D.J. Economou, Effect of transport and reaction on the shape evolution of cavities during wet chemical etching. J. Electrochem. Soc. 136, 1997 (1989).
Acknowledgments
This work was supported by the National Key R&D Program of China Grant Number No. 2019YFB1704600 and the Hubei Provincial Natural Science Foundation of China Grant Number No. 2020CFA032.
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Tang, Y., Li, H., Sheng, J. et al. Study on Wet Chemical Etching of Flexible Printed Circuit Board with 16-μm Line Pitch. J. Electron. Mater. 52, 4030–4036 (2023). https://doi.org/10.1007/s11664-023-10368-z
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DOI: https://doi.org/10.1007/s11664-023-10368-z